Network element and method of communicating using a plurality of controls channels modules

ABSTRACT

A network element forming a mobile communications network, and configured to provide a wireless access interface to one or more communications devices and to transmit downlink data to and receive uplink data from the communications devices via the wireless access interface. The downlink resources extend across a predetermined bandwidth and are time divided into plural timeframes. The network element includes a transmitter, and controller configured to control the transmitter to transmit control data to the communications devices in resources of a control channel formed from plural control channel modules formed from only part of the predetermined bandwidth and mutually exclusive from parts of the predetermined bandwidth from which the other control channel modules are formed. The plural control channel modules allow the control channel to be varied in bandwidth and adapted to the structure of the communications network, the communications devices being served and traffic conditions in the communications network.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on PCT filing PCT/EP2014/072574 filedOct. 21, 2014, and claims priority to European Patent Application 13 191208.1, filed in the European Patent Office on Oct. 31, 2013, the entirecontents of each of which being incorporated herein by reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to network elements for forming part ofmobile communications networks, communications systems, communicationsdevices and methods of communicating data via a wireless accessinterface provided by a mobile communications network.

BACKGROUND OF THE DISCLOSURE

Third as well as fourth generation mobile telecommunication systems,such as those based on the 3GPP defined UMTS and Long Term Evolution(LTE) architecture are able to support more sophisticated services thansimple voice and messaging services offered by previous generations ofmobile telecommunication systems.

For example, with the improved radio interface and enhanced data ratesprovided by LTE systems, a user is able to enjoy on high data rateapplications such as video streaming and video conferencing on mobilecommunications devices that would previously only have been availablevia a fixed line data connection. The demand to deploy fourth generationnetworks is therefore strong and the coverage area of these networks,i.e. geographic locations where access to the networks is possible, isexpected to increase rapidly.

The anticipated widespread deployment of fourth generation networks hasled to the parallel development of a class of communications devices andapplications which, rather than taking advantage of the high data ratesavailable, instead take advantage of the robust radio interface andincreasing ubiquity of the coverage area. Examples include so-calledmachine type communication (MTC) applications, which are typified bysemi-autonomous or autonomous wireless communication devicescommunicating small amounts of data on a relatively infrequent basis.Examples include so-called smart meters which, for example, are locatedin a customer's house and periodically transmit information relating tothe customers consumption of a utility such as gas, water, electricityand so on.

The variety of devices anticipated to operate in LTE systems have arange of different usage requirements and therefore it would bebeneficial if LTE systems are able to provide a wireless accessinterface which can be tailored to the requirements of the differentclasses of devices. For example, high bandwidth devices such assmartphones and tablets may benefit from a wireless access interfacewith a high capacity whereas MTC devices may benefit from a reducedcomplexity lower capacity wireless access interface with a capability totransmit small amounts of data more efficiently, since lower complexitytypically implies lower device cost. A number of approaches currentlyexist to address these problems, for example, by providing aheterogeneous communication network where a number of low-power nodesprovide additional coverage within a coverage area of a high-powerumbrella or macro node, system capacity may be increased. Alternatively,for MTC devices a virtual carrier approach has been proposed where areduced bandwidth segment of the wireless access interface is reservedfor use by MTC devices thus allowing these devices to transmit andreceive data over a reduced bandwidth and in turn lowering theircomplexity and cost.

However, although these approaches each provide a wireless accessinterface tailored to different classes of device, the complexity of theresource allocation associated is potentially complex and may lead toincreased control signalling overheads.

SUMMARY OF THE DISCLOSURE

According to an example embodiment of the present disclosure there isprovided a network element for forming a mobile communications network,the network element configured to provide a wireless access interface toone or more communications devices and to transmit downlink data to andreceive uplink data from the one or more communications devices via thewireless access interface. The downlink resources of the wireless accessinterface extending across a predetermined bandwidth and being dividedin time into a plurality of timeframes. The network element comprising atransmitter and a controller, the controller being configured to controlthe transmitter to transmit control data to the communications devicesin resources of a control channel, wherein the control channel is formeda plurality of control channel modules, each control channel modulebeing formed from a part of the predetermined bandwidth, each of theparts of the predetermined bandwidth from which each of the controlchannels is formed being smaller than the predetermined bandwidth andmutually exclusive from the parts of the predetermined bandwidth fromwhich the other control channel modules are formed.

Providing a control channel formed from a plurality of control channelmodules allows different portions of the control channel to be allocatedto different network elements in a heterogeneous network or differentcommunications devices. This allocation may then reduce the need forcommunications devices to receive the entirety or a significant portionof data within the control channel, thus increasing the efficiency andflexibility of resource allocation. The potentially reduced size of thecontrol channel compared to the predetermined bandwidth of the wirelessaccess interface also provides spare bandwidth, which instead of beingoccupied by the control channel can be used for the provision ofadditional services. Furthermore, physical downlink control channel(PDCCH) information may be contained within a single control channelmodule such that PDCCH information can be detected and decoded withoutreceiving signals from across the entirety of the predeterminedbandwidth.

In one example embodiment each of the control channel modules has asubstantially equal time duration within the frame. Providing thecontrol channel modules with a single duration allows a singleindication of module duration to be provided instead of a separateindication for each control channel module, thus conserving capacity inthe system

In one example each of the control channel modules having unequal timedurations within the frame.

Providing the control channel modules with unequal durations allows theresources dedicated to the control channel to be more flexibilityallocated, thus potential improving the efficiency of the system.

In one example the network element is configured to provide the wirelessaccess interface to communication devices within a first geographicalarea, and the controller is configured to control the transmitter totransmit control data to the communications devices within the firstgeographical area in one of the plurality of control channel modules.

Providing a plurality of control channel modules allows different nodesin a decoupled network to be allocated different control channel modulessuch that communications devices receive control data in a controlchannel module which corresponds to the coverage area in which they arecurrently located. This may therefore reduce the volume of control datathat communications devices are required to receive.

In one example embodiment the bandwidth of the control channel is lessthan the predetermined bandwidth, such that a difference in thebandwidth between the control channel and the predetermined bandwidthprovides a bandwidth gap, wherein the controller is configured tocontrol the transmitter to provide a narrowband virtual carrier in thebandwidth gap.

The provision of a bandwidth gap allows additional services to beprovided to communications devices anywhere in the predetermined systembandwidth where control data would conventionally be situated. Thebandwidth gap may also be utilised to reduce and or avoid interface thusalso increasing the robustness of the wireless access interface.

The provision of a narrowband virtual carrier in the bandwidth gapsallows narrowband devices such as MTC devices to operate within thepredetermined system bandwidth without disrupting the allocation ofcontrol channel resources to conventional communications devices.

In one example embodiment the controller is configured to allocate eachof the control channel modules to communications devices in dependenceupon an identity of each of the communications devices.

The allocation of control channel modules based on the identity of thecommunication devices identity enables a communications device tocalculate the allocation of control channel resources without having toreceive an explicit indication control channel resource allocation.

In one example embodiment the controller is configured to control thetransmitter to provide in a predetermined control module an indicationof the bandwidth and location of the plurality control channel modules.

The provision of a predetermined control channel module enablescommunications devices to obtain an indication of the structure of thecontrol channel without having to receive control channel data acrossthe entirety or a substantial portion of the control channel bandwidth.

Various further aspects and embodiments of the disclosure are providedin the appended claims, including but not limited to a communicationssystem, a communications device and a method of communicating.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described by way ofexample only with reference to the accompanying drawing in which likeparts are provided with corresponding reference numerals and in which:

FIG. 1 provides a schematic diagram of a communications network;

FIG. 2 provides a schematic diagram of an example conventional LTE radioframe;

FIG. 3 provides a schematic diagram of an example conventional LTEsubframe;

FIG. 4 provides a schematic diagram of two example conventional LTEsubframes;

FIG. 5 provides a schematic diagram of an example heterogeneouscommunications network;

FIG. 6 provides a schematic diagram of two LTE subframes in accordancewith an example of the present disclosure;

FIG. 7 provides a schematic diagram of two LTE subframes in accordancewith an example of the present disclosure;

FIG. 8 provides a schematic diagram of two LTE subframes in accordancewith an example of the present disclosure;

FIG. 9 provides a schematic diagram of two LTE subframes in accordancewith an example of the present disclosure;

FIG. 10 provides a schematic diagram of two LTE subframe in accordancewith an example of the present disclosure;

FIG. 11 provides a schematic diagram of two LTE subframe in accordancewith an example of the present disclosure;

FIG. 12 provides a flow diagram of an LTE camp-on procedure inaccordance with an example of the present disclosure; and

FIG. 13 provides a schematic diagram of a communications device and anetwork element in accordance with an example of the present disclosure.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Conventional Network

FIG. 1 provides a schematic diagram illustrating the basic functionalityof a conventional mobile telecommunications network. The networkincludes a plurality of base stations 101 connected to a core network102. Each base station provides a wireless access interface to arespective coverage area 103 (i.e. a cell) within which data can becommunicated to and from mobile terminals 104 via the wireless accessinterface provided by the respective base station. Data is transmittedfrom a base station 101 to a mobile terminal 104 within a coverage area103 via a radio downlink. Data is transmitted from a mobile terminal 104to a base station 101 via a radio uplink. The core network 102 routesdata to and from the mobile terminals 104 and provides functions such asauthentication, mobility management, charging and so on. A mobileterminal may also be referred to as user equipment (UE) or acommunications device and a base station as an enhanced node B (eNodeB)or network element.

Mobile telecommunications systems such as those arranged in accordancewith the 3GPP defined Long Term Evolution (LTE) architecture use anorthogonal frequency division multiplex (OFDM) based interface for theradio downlink (so-called OFDMA) and a single-carrier frequency divisionmultiple access based interface for the radio uplink (so-calledSC-FDMA). Data is transmitted on the uplink and on the downlink on aplurality of orthogonal subcarriers. FIG. 2 shows a schematic diagramillustrating an OFDM based LTE downlink radio frame 201. The LTEdownlink radio frame is transmitted from an LTE base station (known asan enhanced Node B) and lasts 10 ms. The downlink radio frame comprisesten subframes, each subframe lasting 1 ms. A primary synchronisationsignal (PSS) and a secondary synchronisation signal (SSS) aretransmitted in the first and sixth subframes of the LTE frame. Aphysical broadcast channel (PBCH) is located in the first subframe ofthe LTE frame. The PSS, SSS and PBCH are discussed in more detail below.

FIG. 3 provides a schematic diagram providing a grid which illustratesthe structure of an example of a conventional downlink LTE subframe. Thesubframe comprises a predetermined number of symbols which aretransmitted over a 1 ms period. Each symbol comprises a predeterminednumber of orthogonal subcarriers distributed across the bandwidth of thedownlink radio carrier. The example subframe shown in FIG. 3 comprises14 symbols and 1200 subcarriers spaced across a 20 MHz bandwidth. Thesmallest unit on which data can be transmitted in LTE is twelvesubcarriers transmitted over one subframe. For clarity, in FIG. 3, eachindividual resource element is not shown, instead each individual box inthe subframe grid corresponds to twelve subcarriers transmitted on onesymbol. FIG. 3 shows resource allocations for four UEs 340, 341, 342,343 where within these resource allocations signals representing userdata are transmitted from the eNodeB to the UEs. For example, theresource allocation 342 for UE 1 extends over five blocks of twelvesubcarriers, the resource allocation 343 for a second UE 2 extends oversix blocks of twelve subcarriers and so on.

Signals representing control data are transmitted in a control region300 of the subframe comprising the first n symbols of the subframe wheren can vary between one and three symbols for channel bandwidths of morethan 1.4 MHz and where n can vary between two and four symbols forchannel bandwidths of up to and including 1.4 MHz. The control region300 includes a control channel which spans the control region and inwhich data is transmitted on one or more physical downlink controlchannels (PDCCH), the physical control format indicator channel (PCFICH)and the physical HARQ indicator channel (PHICH).

A PDCCH may contain control data common to all UEs or control dataspecific to one or more UEs. The control data may comprise informationto control relevant UEs but also information to indicate whichsubcarriers on which symbols of the subframe have been allocated to datafor UEs. Each PDCCH conveys one instance of a downlink controlinformation (DCI) and is interleaved across the control channel,therefore a receiver is required to receive signals from across theentire control region in order to decode data conveyed by a PDCCHs Forexample, PDCCH data transmitted in the control region 300 of thesubframe shown in FIG. 3 would indicate that UE1 has been allocated thefirst block of resources 342, that UE2 has been allocated the secondblock of resources 343, and so on. In subframes where it is transmitted,the PCFICH contains control data indicating the duration of the controlregion in that subframe (i.e. between one and four symbols) and thePHICH contains HARQ (Hybrid Automatic Request) data indicating whetheror not previously transmitted uplink data has been successfully receivedby the network.

In certain subframes, symbols in a central band 310 of the subcarriersare used for the transmission of information including the PSS, the SSSand the PBCH mentioned above. This central band 310 is typically 72subcarriers wide (corresponding to a transmission bandwidth of 1.08MHz). The PSS and SSS are synchronisation sequences that once detectedallow a communications terminal 104 to achieve frame synchronisation anddetermine the cell identity of the eNodeB transmitting the downlinksignal. The PBCH carries information about the cell, comprising a masterinformation block (MIB) that includes parameters that the communicationsterminals require to access the cell. The data transmitted to individualcommunications terminals on the physical downlink shared channel (PDSCH)can be transmitted in the remaining blocks of communications resourceelements of the subframe.

FIG. 3 also shows a region of PDSCH containing system information andextending over a bandwidth of R₃₄₄. Thus in FIG. 3 the central frequencycarries control channels such as the PSS, SSS and PBCH and thereforeimplies a minimum bandwidth of a receiver of a communications terminal.

The number of subcarriers in an LTE channel can vary depending on theconfiguration of the transmission network. Typically this variation isfrom 72 sub carriers contained within a 1.4 MHz channel bandwidth to1200 subcarriers contained within a 20 MHz channel bandwidth as shown inFIG. 3. As is known in the art, subcarriers carrying data transmitted onthe PDCCHs, PCFICH and PHICH are typically distributed across the entirebandwidth of the subframe. Therefore a conventional communicationsterminal must be able to receive the entire bandwidth of the subframe inorder to receive and decode the control region.

FIG. 4 provides a simplified diagram of a downlink subframe where acontrol channel and the PDSCH are shown. In FIG. 4, each subframe has asingle PDCCH 401 in the control channel which spans a predetermined timeperiod represented by n OFDM symbols and a PDSCH 402 which spanssubstantially the entire system bandwidth represented by y resourceblocks. The form of subframe in FIG. 4 is primarily designed for systemswhere there is a central eNodeB and both user data and control data aretransmitted and received in the uplink and downlink by the eNodeB.However, restricting a system to operate in this manner may limit theflexibility and achievable data rates in the system. For example, due tothe limited transmission power at a UE, it may be beneficial for the UEto transmit data to a local low-power node which then communicates thedata to the central eNodeB but still receive control data directly fromthe high-power serving eNodeB. Furthermore, the low-power node may alsotransmit downlink user data to the UE thus relieving the central eNodeBof this task.

FIG. 5 provides a diagram of an example system where a first high-powereNodeB 501 provides a first coverage area 502 and a second low-powernode 503 provides a second coverage area 504 which is smaller than andwithin the first coverage area 502. The node 502 may also be referred toas an umbrella or macro node and node 503 as a local or low-power nodewhere the macro node provides coverage between the areas served by thelocal low-power nodes. The UE 505 is within both the first and secondcoverage areas and therefore is capable of communicating with both thecentral eNodeB 501 and the lower power node 503. A proportion of thecontrol signalling is centrally transmitted from the eNodeB 501 to theUE, this signalling is common control signalling which multiple UEs inthe cell 502 are required to receive and is represented by arrow 506. UEspecific control signal is transmitted locally from the low power node503 to the UE 505 and is represented by the dashed arrow 507 where theconnection between the low-power node 503 and the eNodeB 501 may beprovided by a backhaul connection. Although the macro node and thelow-power node may transmit different control data, synchronisationsignals broadcast signals and reference signals may stay the samebetween the macro node and the low-power node, for example PSS, SSS andPBCH signals may be common between the nodes. The UE specific user datais also transmitted locally from the low-power node and is representedby arrow 508 where once again the connection between the low-power node503 and the eNodeB 501 may be provided by a backhaul connection. Thisdecoupled arrangement can be lead to increases in capacity as the eNodeBis not required to transmit all UE user data within the coverage area502. Instead a proportion of the UE user data is transmitted by lowpower local nodes such as 503. However this increase in capacity cancome at the cost of increased control signalling and coordinationbetween nodes and therefore may lead to control signalling overload atthe eNodeB. In some examples the structure of FIG. 5 may correspond to aheterogeneous network where the low-power node 503 may be referred to asa pico node or femto node. Pico or femto nodes may be placed in areaswhere there is particularly high demand in order to increase capacity tobeyond the capacity that can be achieved with a single high-power node.

In accordance with the present disclosure a flexible control channel isprovided which allows the control channel in LTE systems to be tailoredto the structure of the cell or coverage area in which it is being used.This flexibility thus allows the control channel to be adapted such thatthe likelihood of control overload can be reduced and transmission ofcontrol data more evenly and efficiently distributed between servingeNodeBs and local lower power nodes. As described with reference toFIGS. 3 and 4, the existing control channel and the one or more PDCCHscontained therein can only be dimensioned in time i.e. can vary induration from one to four OFDM symbols depending on the number ofsubcarriers being utilised in the system. In accordance with the presentdisclosure one or more control channel modules which form the controlchannel are provided and can be dimensioned in the frequency domain suchthat the control channel is not restricted to a single continuous regionspanning substantially the entire bandwidth of the system as illustratedin FIGS. 3 and 4. The control channel modules may span mutuallyexclusive bandwidths and may allow one or more PDCCHs to be fullycontained within a single control channel module such that PDCCHs may bereceived without receiving signals across the entire bandwidth of thecontrol region. Furthermore, each control channel module is formed frompart of the control region (i.e. predetermined system bandwidth)bandwidth, where the part of the system bandwidth which forms eachcontrol channel modules is smaller than the system bandwidth.

FIG. 6 provides a schematic diagram of a control channel structure inaccordance with an example embodiment of the present disclosure, whereeach control channel module contains a single PDCCH. However, eachcontrol channel module may also contain more than one PDCCH. Instead ofa single continuous control channel in which PDCCHs are located, thecontrol channel is formed from one or more independent control channelmodules, where in the subframes of FIG. 6 the control channel is formedfrom two control channel modules 601 and 602, each of which have anon-overlapping bandwidth less then the bandwidth of the system. Thesecontrol channel modules may then be allocated to different nodes, forexample an eNodeB and a low-power node as described with reference toFIG. 5. PDCCH data in each of the modules may then indicate theresources in the PDSCH 603 which have been allocated to the UE served bythe nodes. Consequently, the PDCCH data may be received withoutreceiving signals from across substantially the entire control region,in contrast to the case in existing LTE systems. Implementation of thisflexible allocation may therefore require a revised mapping of resourceelements to PDCCHs in the control modules compared to existing LTEcontrol structures. The modular structure of the control channel allowsthe transmission of control data to be split between one or more nodeswhich may operate over same frequency so that the likelihood of controlsignalling overload at a node is reduced. This may be advantageous inheterogeneous networks where a single high power node is unable toprovide sufficient capacity and a further node i.e. 503 has beenintroduced in order to increase capacity. The structure of the controlchannel may be dynamically controlled by the eNodeB so that it can beadapted to suit the current or expected traffic conditions of thenetwork. For example, if a large number of devices within area 504become active the size control channel module 602 which is allocated tolow-power node 503 may be increased and the size of control channelmodule 601 decreased, thus providing more capacity for control data fromthe low-power node 503. In some examples, the different control channelmodules may be allocated to different classes of devices, for instancemodule 601 may be allocated to high-bandwidth devices and 602 may beallocated to low-bandwidth devices.

In FIG. 6 the control channel modules 601 and 602 are each smaller inbandwidth that the bandwidth of the system (y resources blocks) but intotal are approximately equal or equal to the system bandwidth. Morespecifically control channel module 601 spans a bandwidth of x resourceblocks (12 x subcarriers) and control channel module 602 spans kresource blocks (12 k subcarriers), where y=x+k. The division of theconventional control channel bandwidth into a number of independentcontrol channel modules may in some examples result in legacy devicesbeing unable to operate with the newly proposed modular formationbecause of the non-contiguous nature of the proposed control channel andthe fact that PDCCHs may no longer be interleaved over substantially theentire bandwidth of the system. However, this may be overcome by theeNodeB switching between the existing control channel structure and theproposed control channel structure, and signalling any such switching toUEs being served. The control channel modules may be of a singleduration in time or their duration may vary with respect to each other.The duration and/or bandwidth of the control channel modules may besignalled in a module-specific PCFICH, signalled in a common PCFICH orbe included in a commonly received default control channel module whichis described in more detail below.

FIG. 7 provides a schematic diagram of a control channel structure inaccordance with another example embodiment of the present disclosure.The control channel is formed from a single control channel module 701which has a bandwidth of x resource blocks where x is less than thebandwidth y of the system and the single control channel module may actas a reduced bandwidth PDCCH. As a result of x<y there is a bandwidthgap 702 of width k resource blocks between the control channel formedfrom the channel module 701 and the predetermined bandwidth of thesystem. This bandwidth gap may have a number of applications, forinstance in may be used to provide auxiliary services, be used to servenarrowband devices or used as a frequency notch in order to reduceinterface to other co-existing systems or avoid interference caused byco-existing systems. Alternatively, if network traffic in a system islow the total bandwidth of the control channel can be reduced andtherefore for the bandwidth gap increases so that UE is required toreceive a smaller bandwidth, thus reducing power consumption.

FIG. 8 provides a schematic diagram of a control channel structure wherethe bandwidth gap described with reference to FIG. 7 has been utilisedto provide a narrowband virtual carrier 801. A virtual carrier is anexisting technique directed towards serving low-cost and low-complexitydevices such as machine-type communications (MTC) devices as describedin a number of co-pending patent applications GB 1101970.0, GB1101981.7, GB 1101966.8, GB 1101983.3, GB 1101853.8, GB 1101982.5, GB1101980.9 and GB 1101972.6, the contents of which are incorporatedherein by reference. The use of a narrowband virtual carrier reduces therequired operational bandwidth of a device's receiver thus in turnreducing the cost of such devices. The use of virtual carriers with MTCdevices allows these devices to operate alongside convention LTEdevices, such as smartphones and tablets, with out requiring the samecapabilities as conventional LTE devices. In order to implement thenarrowband virtual carrier of FIG. 8, appropriate PDSCH scheduling willbe required in order to ensure that conventional non-virtual carrierdevices are not allocated PDSCH resources which fall within the virtualcarrier bandwidth. Although in FIG. 8 the virtual carrier is positionedat the upper end of the predetermined system bandwidth it may be locatedat any point in the system bandwidth and in some examples more than onenarrowband virtual carrier may be provided when one or more bandwidthgaps are provided.

FIG. 9 provides a schematic diagram of an example embodiment of amodular control channel structure when a plurality of nodes are eachallocated a control channel module. The structure of the control channelin FIG. 9 has been adapted for use in scenarios such as that illustratedin FIG. 5 but the structure may be adapted for use where there is aplurality of low-power nodes serving under a single macro node. Thecontrol channel is formed from three control channel modules 901, 902and 903. The control channel module 901 is allocated to the low-powernode 503 for transmission of control data specific to devices servingthe low-power node 503 and the control channel module 902 is allocatedto the macro or high-power eNodeB 501 for transmission of control dataspecific to devices served by the macro node 501. The default controlchannel module 903 is allocated for transmission of control channel datarequired by all devices and may provide control information common tothe macro cell and the small cell. Initially when a UE attempts toconnect to the cell it will decode the default control informationtransmitted in control channel module 903, the default controlinformation indicating for example the location and size of the othercontrol channel modules and their relationship with the nodes 501 and503. The UE will then subsequently decode the control information in theappropriate control channel module, for example module 901 if in area501 or 903 if in area 504. The default control channel module 903 islikely to be transmitted by high-power node 501 such that it can bereceived by UEs throughout the cell area 502 but in some examples it maybe transmitted by the low-power node 503. The modular arrangementillustrated in FIG. 9 advantageously reduces the volume of schedulingdata the node 501 is required to transmit and therefore reduces thelikelihood that the node 501 encounters a control data overload. Commonsearch space downlink control information may be provided in the macrocontrol channel module 903 and UE-specific search space downlink controlinformation provided in the macro control channel 903 or the low-powernodes control channel module 902 depending on the node serving a UE withdownlink user data.

FIG. 10 provides a schematic diagram of an example embodiment where thecontrol channel is formed from a plurality of control channel modules.This arrangement allows control channel modules to be allocated tonumerous nodes and or UEs. In FIG. 10 the control channel is formed fromcontrol channel modules 1001, 1002, and 1003 and up to control channelmodule m 1004. Each control channel module may be allocated to differententities, for instance UEs based on their radio network temporaryidentifier (RNTI), and the allocation criteria broadcast in a defaultcontrol channel module or provided in system specifications.Restrictions may be placed on the serving eNodeB such that controlchannel modules allocated for a given RNTI may only span across resourceblocks with the control channel bandwidth which satisfy a function ofthe RNTI. For instance, control channel modules for a particular RNTImay start and span resource blocks satisfying a modulo division of theRNTI. For example, a control channel module may start in resource blockswhere RNIT mod 3=0 and span a number of resource blocks where RNTI mod3=0. Although this approach increases the restrictions on controlchannel module allocation and may increase complexity at the eNodeB, itmay simplify the process of searching for relevant control channelmodules by the UEs, thus reducing their power consumption.

In FIG. 10 the maximum number of control channel modules is limited bytheir minimum size e.g. in Release-11 LTE specifications six resourceblocks, and the maximum allowable bandwidth of the control channel. Forinstance the maximum number of control channel modules may be equal tothe number of Resource Blocks in Maximum Bandwidth/6 where the minimumsize of a control channel module is six resource blocks. As illustratedin FIG. 10 the control channel modules may be of varying sizes such thatthe eNodeB can allocate larger control channel modules to UEs or nodesrequiring comparatively more control channel data. Although the controlchannel modules may be allocated on an individual UE or node basis, amodule containing common search space downlink control information maybe provided which includes common control data such as paging and randomaccess responses. The location of such a control channel module may bestated in system specifications or signalled in broadcast data such assystem information blocks.

FIG. 11 provides a schematic diagram of an example embodiment where thecontrol channel is formed from a plurality of control channel modulesand a bandwidth gap in the control channel has been left in between thecontrol channel modules for the insertion of a narrowband virtualcarrier. In FIG. 11 the control channel is formed from four controlchannel modules 1101 to 1104 where a bandwidth gap is provided betweencontrol channel modules 1103 and 1104. In an analogous manner to thatdescribed with reference to FIG. 8, a narrowband virtual carrier thenmay be inserted in the bandwidth gap. Once again appropriate schedulingfor the PDSCH will be also be required in order for clear space in thePDSCH to be allocated to the virtual carrier. The adaptable nature ofhaving a plurality of independent control channel modules enables one ormore virtual carriers to be inserted into any portion of the systembandwidth as opposed to a set position which cannot be varied by theeNodeB. The adaptable placement and size of the control channel modulesalso allows the virtual carrier to variable in size without requiringexcess unused bandwidth in the control channel. For instance, a virtualcarrier bandwidth may be varied between 24 and 18 resources blocks insome examples such that when the virtual carrier bandwidth is reduced to18 blocks from 24 blocks, the control channel modules can be adapted andrearranged to utilise these extra resource blocks.

In some implementations of the preceding example embodiments a defaultcontrol channel module may be provided in which the eNodeB transmitssystem information. These default control channel modules provide UEswith data required to initially camp-on to the cell without having to doperform blind decoding on all possible module sizes and the datacontained in each module. The default control channel module may alsoprovide information on the structure of the control channel modulesincluding their beginning and end and the location of any blank controlchannel modules such that superfluous decoding and blind detection canbe reduced. The location of the default control channel module may behardcoded or signalled in broadcast system information and firstacquired when camping-on to the wireless access interface. Additionalcontrol channel structure information may be signalled using the masterinformation block where the system frame number, system bandwidth andcontrol channel size can be indicated. Alternatively, using the PCFICHthe number of control channel symbols and control channel size can beindicated.

FIG. 12 provides a flow diagram illustrating an example camp-onprocedure of a UE and the initial stages in reception of controlinformation when the control channel is formed from one or more controlchannel modules and a default control channel module is utilised toprovide control channel structure information to UEs. This procedureincludes the following steps at the UE

S1201: Acquiring the frequency of the serving eNodeB;

S1202: Detecting the primary synchronisation signal (PSS) in order toobtain slot timing and SSS scrambling code;

S1203: Detecting the secondary synchronisation signal (SSS) in order toobtain frame timing and cell group ID sequence;

S1204: Calculating the cell ID using PSS and SSS;

S1205: Detecting the reference signal location using cell ID;

S1206: Detecting the master information block (MIB) in the PBCH;

S1207: Detecting size of the default control channel model using theMIB, system frame number and system bandwidth;

S1208: Decoding PCFICH and detecting symbols allocated to the controlchannel;

S1209: Decoding downlink control information for system informationblock 1 from default control channel module;

S1210: Decoding system information block 1 and detecting size ofcorresponding control channel module which includes schedulinginformation for other SIBs;

S1211: Decoding other system information blocks;

The above procedure may include additional steps required to camp-on toan eNodeB and or some steps may be performed in a different order. Forinstance, it is possible that the size of the default control channelmodule may be detected at step S1208 instead of S1207.

FIG. 13 provides a schematic diagram of a UE 1301 and an eNodeB 1305 inwhich example embodiments of the present techniques may be implemented.The UE includes a transmitter 1302, a receiver 1303 and a controller1304 where the controller is configured to control the receiver 1303 todetect signals representing the control data and user data transmittedby the eNodeB 1305, and to estimate the data conveyed by the signals.The controller 1304 is also configured to control the transmitter 1302to transmit signals representing uplink data to the eNodeB. As well asdetecting signals transmitted by the eNodeB 1305, the UE 1301 may alsodetect signals transmitted by a low-power node or other network element.The eNodeB 1305 includes a transmitter 1306, a receiver 1307 and acontroller 1308, where the controller 1308 is configured to control thetransmitter 1306 to transmit signals representing control data and userdata to the UE 1301. The controller 1308 is also configured to controlthe receiver 1307 to detect signals representing user uplink data andestimate the data conveyed by these signals. The controller at theeNodeB may dynamically control the structure of the modular controlchannel via broadcast messages or messages contained in default controlchannel modules, such that the structure of the control channel can beadapted to suit the current or expected traffic conditions in thenetwork. The eNodeB when operating as a macro cell as illustrated inFIG. 5, may communicate control data via the wireless access interfaceto all nodes within its coverage area but also communicate control datato the low-power node via a backhaul link for transmission.Alternatively, the low-power node may perform some or all of thescheduling tasks and transmit this control data directly to the UEswithin its coverage area.

The following numbered paragraphs provide further example aspects andfeature of the present technique:

Paragraph 1. A network element for forming a mobile communicationsnetwork, the network element comprising

a transmitter configured to transmit signals via a wireless accessinterface to one or more communications devices,

a receiver configured to receive signals from the one or morecommunications devices via the wireless access interface, and

a controller configured to control the transmitter and the receiver toform the wireless access interface, the wireless access interfaceincluding downlink resources extending across a predetermined bandwidthand being divided in time into a plurality of frames, and to control thetransmitter

to transmit control data to the communications devices in resources of acontrol channel, wherein the control channel is formed from a pluralityof control channel modules, each control channel module being formedfrom a part of the predetermined bandwidth, the part of thepredetermined bandwidth of each control channel module being less thanthe predetermined bandwidth and mutually exclusive from the parts of thepredetermined bandwidths from which the other control channel modulesare formed.

Paragraph 2. A network element according to paragraph 1, wherein theplurality of control channel modules each have a substantially equaltime duration within the frame.

Paragraph 3. A network element according to paragraph 1 or 2, wherein atleast one of the plurality of control channel modules has a timeduration unequal to at least one other of the plurality of the controlchannel modules within the frame.

Paragraph 4. A network element according to paragraph 1, 2 or 3, whereinthe network element is configured to provide the wireless accessinterface to communication devices within a first geographical area, andthe controller is configured to control the transmitter to transmit thecontrol data to the communications devices within the first geographicalarea in a control channel module from the plurality of control channelmodules.

Paragraph 5. A network element according to any of paragraphs 1 to 4,wherein a bandwidth occupied by the plurality of control channel modulesis less than the predetermined bandwidth, such that a difference in thebandwidth occupied by the plurality of control channel modules and thepredetermined bandwidth provides a bandwidth gap, wherein the controlleris configured to control the transmitter to provide a narrowband virtualcarrier in the bandwidth gap.

Paragraph 6. A network element according to any of paragraphs 1 to 5,wherein the controller is configured to allocate each of the controlchannel modules to communications devices in dependence upon an identityof each of the communications devices.

Paragraph 7. A network element according to any of paragraphs 1 to 6,wherein the controller is configured to control the transmitter toprovide in a predetermined one of the plurality of control modules anindication of the bandwidth and the location of each of the plurality ofthe other control channel modules.

Paragraph 8. A communications device for communicating with a networkelement of a communications network, the network element configured toprovide a wireless access interface to the communications device, thecommunications device comprising

a transmitter configured to transmit uplink signals to the networkelement via the wireless access interface,

a receiver configured to receive downlink signals from the networkelement via the wireless access interface via downlink resources of thewireless access interface, the wireless access extending across apredetermined bandwidth and being divided in time into a plurality offrames, and

a controller configured to control the receiver

to detect control data transmitted by the network element in a controlchannel of the wireless access interface, wherein the control channel isformed from a plurality of control channel modules, each control channelmodule being formed from a part of the predetermined bandwidth, the partof the predetermined bandwidth of each control channel module being lessthan the predetermined bandwidth and mutually exclusive from the partsof the predetermined bandwidths from which the other control channelmodules are formed.

Paragraph 9. A communications device according to paragraph 8, wherein apredetermined control channel module provides an indication of thebandwidth and the location of each of the plurality of the other controlchannel modules and the controller is configured to control the receiverto detect the indication from the predetermined control channel and todetect the control data from another control channel module of theplurality of control channel modules based on the indication.

Paragraph 10. A communications system comprising a mobile communicationsnetwork and a communications device for communicating via the mobilecommunications network, the mobile communications network including

a network element configured to transmit signals using a transmitter viaa wireless access interface to the communications device, to receivesignals using a receiver from the communications device via the wirelessaccess interface, and to control the transmitter and the receiver toform the wireless access interface, the wireless access interfaceincluding downlink resources extending across a predetermined bandwidthand being divided in time into a plurality of frames, and to control thetransmitter

to transmit control data to the communications device in resources of acontrol channel, wherein the control channel is formed from f aplurality of control channel modules, each control channel module beingformed from a part of the predetermined bandwidth, the part of thepredetermined bandwidth of each control channel module being less thanthe predetermined bandwidth and mutually exclusive from the parts of thepredetermined bandwidths from which the other control channel modulesare formed.

Paragraph 11. A communications system according to paragraph 10, whereinthe plurality of control channel modules each have a substantially equaltime duration within the frame.

Paragraph 12. A communications system according to paragraph 10 or 11,wherein at least one of the plurality of control channel modules has atime duration unequal to at least one other of the plurality of thecontrol channel modules within the frame.

Paragraph 13. A communications system according to paragraph 10, 11 or12, wherein the network element is configured to provide the wirelessaccess interface to the communication device within a first area, andthe controller is configured to control the transmitter to transmit thecontrol data to the communications device within the first area in thecontrol channel module from the plurality of control channel modules.

Paragraph 14. A communications system according to paragraph 10, 11 12,or 13, wherein a bandwidth occupied by the plurality of control channelmodules is less than the predetermined bandwidth, such that a differencein the bandwidth occupied by the plurality of control channel modulesand the predetermined bandwidth provides a bandwidth gap during thepredetermined time period, wherein the controller is configured tocontrol the transmitter to provide a narrowband virtual carrier withinthe bandwidth gap.

Various further aspects and features of the present invention aredefined in the appended claims and various combinations of the featuresof the dependent claims may be made with those of the independent claimsother than the specific combinations recited for the claim dependency.Modifications may also be made to the embodiments hereinbefore describedwithout departing from the scope of the present invention. For instance,although a feature may appear to be described in connection withparticular embodiments, one skilled in the art would recognise thatvarious features of the described embodiments may be combined inaccordance with the disclosure.

The invention claimed is:
 1. A network element for forming a mobilecommunications network, the network element comprising: a transmitterconfigured to transmit downlink signals to a plurality of communicationsdevices; a receiver configured to receive uplink signals from theplurality of communications devices; and a controller configured tocontrol the transmitter to transmit the downlink signals, using controlchannel resources of a control channel, the control channel resourcesextending across a predetermined bandwidth in a frequency domain andbeing divided in time in a time domain into a plurality of subframesincluding at least a first subframe and a second subframe, control thetransmitter to transmit control data to the plurality of communicationsdevices using the control channel resources of the control channel,wherein the control channel resources of the control channel comprise aplurality of control channel modules including at least a first controlchannel module, a second control channel module, a third control channelmodule, and a fourth control channel module, each control channel moduleof the plurality of control channel modules is uniquely allocated to acorresponding communications device of the plurality of communicationsdevices, the first control channel module and the second control channelmodule extend across a first time duration in the time domain within thefirst subframe, the first control channel module extends across a firstpart of the predetermined bandwidth in the frequency domain, and thesecond control channel module extends across a second part of thepredetermined bandwidth in the frequency domain, the first part and thesecond part of the predetermined bandwidth not overlapping in thefrequency domain, the third control channel module and the fourthcontrol channel module extend across a second time duration in the timedomain within the second subframe, the second time duration notoverlapping the first time duration in the time domain, and the thirdcontrol channel module extends across the first part of thepredetermined bandwidth in the frequency domain, and the fourth controlchannel module extends across the second part of the predeterminedbandwidth in the frequency domain.
 2. The network element as claimed inclaim 1, wherein the plurality of control channel modules each have asubstantially equal time duration within a subframe of the plurality ofsubframes.
 3. The network element as claimed in claim 1, wherein theplurality of communication devices are within a first geographical area.4. The network element as claimed in claim 1, wherein a bandwidthoccupied by the plurality of control channel modules is less than thepredetermined bandwidth such that a difference in the bandwidth and thepredetermined bandwidth provides a bandwidth gap, and the controller isconfigured to control the transmitter to provide a narrowband virtualcarrier in the bandwidth gap.
 5. The network element as claimed in claim1, wherein the controller is configured to allocate the each controlchannel module of the plurality of control channel modules to thecorresponding communications device of the plurality of communicationsdevices in dependence upon an identity of each of the plurality ofcommunications devices.
 6. The network element as claimed in claim 1,wherein the controller is configured to control the transmitter toprovide, in a predetermined control channel module of the plurality ofcontrol channel modules, an indication of a bandwidth and a location ofeach of the plurality of the other control channel modules.
 7. Acommunications device for communicating with a network element of acommunications network, the communications device comprising: atransmitter configured to transmit uplink signals to the networkelement; a receiver configured to receive downlink signals from thenetwork element using control channel resources of a control channel,the control channel resources extending across a predetermined bandwidthin a frequency domain and being divided in time in a time domain into aplurality of subframes including at least a first subframe and a secondsubframe; and a controller configured to control the receiver to detectcontrol data transmitted by the network element in the control channel,wherein the control channel resources of the control channel comprise aplurality of control channel modules including at least a first controlchannel module, a second control channel module, a third control channelmodule, and a fourth control channel module, each control channel moduleof the plurality of control channel modules is uniquely allocated to acorresponding communications device of a plurality of communicationsdevices, the plurality of communications devices including thecommunications device, the first control channel module and the secondcontrol channel module extend across a first time duration in the timedomain within the first subframe, the first control channel moduleextends across a first part of the predetermined bandwidth in thefrequency domain, and the second control channel module extends across asecond part of the predetermined bandwidth in the frequency domain, thefirst part and the second part of the predetermined bandwidth notoverlapping in the frequency domain, the third control channel moduleand the fourth control channel module extend across a second timeduration in the time domain within the second subframe, the second timeduration not overlapping the first time duration in the time domain, andthe third control channel module extends across the first part of thepredetermined bandwidth in the frequency domain, and the fourth controlchannel module extends across the second part of the predeterminedbandwidth in the frequency domain.
 8. The communications device asclaimed in claim 7, wherein a predetermined control channel moduleprovides an indication of a bandwidth and a location of each of theplurality of the other control channel modules, and the controller isconfigured to control the receiver to detect the indication from thepredetermined control channel module and to detect the control data fromanother control channel module of the plurality of control channelmodules based on the indication.
 9. A communications system comprising:a plurality of communications devices for communicating via a mobilecommunications network; and a network element configured to transmitdownlink signals using a transmitter to the plurality of communicationsdevices, receive uplink signals using a receiver from the plurality ofcommunications devices, control the transmitter to transmit the downlinksignals, using control channel resources of a control channel, thecontrol channel resources extending across a predetermined bandwidth ina frequency domain and being divided in time in a time domain into aplurality of subframes including at least a first subframe and a secondsubframe, control the transmitter to transmit control data to theplurality of communications devices using the control channel resourcesof the control channel, wherein the control channel resources of thecontrol channel comprise a plurality of control channel modulesincluding at least a first control channel module, a second controlchannel module, a third control channel module, and a fourth controlchannel module, each control channel module of the plurality of controlchannel modules is uniquely allocated to a corresponding communicationsdevice of the plurality of communications devices, the first controlchannel module and the second control channel module extend across afirst time duration in the time domain within the first subframe, thefirst control channel module extends across a first part of thepredetermined bandwidth in the frequency domain, and the second controlchannel module extends across a second part of the predeterminedbandwidth in the frequency domain, the first part and the second part ofthe predetermined bandwidth not overlapping in the frequency domain, thethird control channel module and the fourth control channel moduleextend across a second time duration in the time domain within thesecond subframe, the second time duration not overlapping the first timeduration in the time domain, and the third control channel moduleextends across the first part of the predetermined bandwidth in thefrequency domain, and the fourth control channel module extends acrossthe second part of the predetermined bandwidth in the frequency domain.10. The communications system as claimed in claim 9, wherein theplurality of control channel modules each have a substantially equaltime duration within a subframe of the plurality of subframes.
 11. Thecommunications system as claimed in claim 9, wherein the plurality ofcommunication devices are within a first geographical area.
 12. Thecommunications system as claimed in claim 9, wherein a bandwidthoccupied by the plurality of control channel modules is less than thepredetermined bandwidth such that a difference in the bandwidth and thepredetermined bandwidth provides a bandwidth gap, and the controller isconfigured to control the transmitter to provide a narrowband virtualcarrier within the bandwidth gap.
 13. A method of communicating via amobile communications network, the method comprising: transmittingdownlink signals to a plurality of communications devices; receivinguplink signals from the plurality of communications devices; controllingthe transmitting and the receiving using control channel resources of acontrol channel, the control channel resources extending across apredetermined bandwidth in a frequency domain and being divided in timein a time domain into a plurality of subframes including at least afirst subframe and a second subframe; transmitting control data to theplurality of communications devices using the control channel resourcesof the control channel, wherein the control channel resources of thecontrol channel comprise a plurality of control channel modulesincluding at least a first control channel module, a second controlchannel module, a third control channel module, and a fourth controlchannel module, each control channel module of the plurality of controlchannel modules is uniquely allocated to a corresponding communicationsdevice of the plurality of communications devices, the first controlchannel module and the second control channel module extend across afirst time duration in the time domain within the first subframe, thefirst control channel module extends across a first part of thepredetermined bandwidth in the frequency domain, and the second controlchannel module extends across a second part of the predeterminedbandwidth in the frequency domain, the first part and the second part ofthe predetermined bandwidth not overlapping in the frequency domain, thethird control channel module and the fourth control channel moduleextend across a second time duration in the time domain within thesecond subframe, the second time duration not overlapping the first timeduration in the time domain, and the third control channel moduleextends across the first part of the predetermined bandwidth in thefrequency domain, and the fourth control channel module extends acrossthe second part of the predetermined bandwidth in the frequency domain.14. Circuitry for a network element for forming a mobile communicationsnetwork, the circuitry comprising: transmitter circuitry configured totransmit downlink signals to a plurality of communications devices;receiver circuitry configured to receive uplink signals from theplurality of communications devices; and controller circuitry configuredto control the transmitter circuitry to transmit the downlink signals,using control channel resources of a control channel, the controlchannel resources extending across a predetermined bandwidth in afrequency domain and being divided in time in a time domain into aplurality of subframes including at least a first subframe and a secondsubframe, control the transmitter circuitry to transmit control data tothe plurality of communications devices using the control channelresources of the control channel, wherein the control channel resourcesof the control channel comprise a plurality of control channel modulesincluding at least a first control channel module, a second controlchannel module, a third control channel module, and a fourth controlchannel module, each control channel module of the plurality of controlchannel modules is uniquely allocated to a corresponding communicationsdevice of the plurality of communications devices, the first controlchannel module and the second control channel module extend across afirst time duration in the time domain within the first subframe, thefirst control channel module extends across a first part of thepredetermined bandwidth in the frequency domain, and the second controlchannel module extends across a second part of the predeterminedbandwidth in the frequency domain, the first part and the second part ofthe predetermined bandwidth not overlapping in the frequency domain, thethird control channel module and the fourth control channel moduleextend across a second time duration in the time domain within thesecond subframe, the second time duration not overlapping the first timeduration in the time domain, and the third control channel moduleextends across the first part of the predetermined bandwidth in thefrequency domain, and the fourth control channel module extends acrossthe second part of the predetermined bandwidth in the frequency domain.15. Circuitry for communicating with a network element of acommunications network, the circuitry comprising: transmitter circuitryconfigured to transmit uplink signals to the network element; receivercircuitry configured to receive downlink signals from the networkelement using control channel resources of a control channel, thecontrol channel resources extending across a predetermined bandwidth ina frequency domain and being divided in time in a time domain into aplurality of subframes including at least a first subframe and a secondsubframe, and controller circuitry configured to control the receivercircuitry to detect control data transmitted by the network element inthe control channel, wherein the control channel resources of thecontrol channel comprise a plurality of control channel modulesincluding at least a first control channel module, a second controlchannel module, a third control channel module, and a fourth controlchannel module, each control channel module of the plurality of controlchannel modules is uniquely allocated to a corresponding communicationsdevice of a plurality of communications devices, the plurality ofcommunications devices including the communications device, the firstcontrol channel module and the second control channel module extendacross a first time duration in the time domain within the firstsubframe, the first control channel module extends across a first partof the predetermined bandwidth in the frequency domain, and the secondcontrol channel module extends across a second part of the predeterminedbandwidth in the frequency domain, the first part and the second part ofthe predetermined bandwidth not overlapping in the frequency domain, thethird control channel module and the fourth control channel moduleextend across a second time duration in the time domain within thesecond subframe, the second time duration not overlapping the first timeduration in the time domain, and the third control channel moduleextends across the first part of the predetermined bandwidth in thefrequency domain, and the fourth control channel module extends acrossthe second part of the predetermined bandwidth in the frequency domain.